The present invention relates to a high-performance aspherical zoom lens having a wide half angle of view of about 32.degree.-35.degree. at a wide angle end, and a video camera employing the zoom lens.
In response to recent demand for excellent operational efficiency, good mobility and high image quality in video cameras, high-resolution imaging devices as compact as 1/3" are becoming a mainstream of imaging devices. Meanwhile, in this connection, high-performance and high-magnification zoom lenses which are large in aperture ratio, compact in size and light in weight are in strong demand. Furthermore, due to a big demand for reduction of production costs of zoom lenses, high-performance wide angle zoom lenses in which the number of lens components is reduced are in urgent need.
However, in known wide angle zoom lenses, not only have the diameters of lenses of a first lens group become excessively large, but a large number of lenses are currently required used for performing more strict aberration correction. As a result, the known wide angle zoom lenses have become larger, heavier and more expensive and therefore, have not been suitable for use in video cameras for home use. Therefore, the half angle of view of known compact and light zoom lenses having an F-number of about 1.4 to 1.6 and including lenses about 10 to 13 lenses is 25.degree. or less.
Hereinbelow, one example of a prior art zoom lens for use in a video camera disclosed in, for example, U.S. Pat. No. 5,100,223 is described with reference to FIG. 2. The prior art zoom lens includes a first lens group 21 acting as an image forming portion, a second lens group 22 acting as a magnification changing portion, a third lens group 23 acting as a light converging portion, a fourth lens group 24 acting as a focusing portion and a glass plate 25 optically equivalent to a quartz crystal filter and a face plate of an imaging device. Reference numeral 26 denotes an image surface.
Operation of the prior art zoom lens of the above described arrangement is described hereinbelow. The first lens group 21 is fixed relative to the image surface 26 and has an image forming function, while the second lens group 22 is movable along an optical axis A so as to change the magnification such that a focal length of the entire system is changed. The third lens group 23 is fixed relative to the image surface 26 and has a function of converging divergent light produced by the second lens group 22. On the other hand, the fourth lens group 24 is movable along the optical axis A and has a focusing function. Variations in position of the image surface 26 due to travel of the second lens group 22 at the time of zooming are eliminated by displacing the fourth lens group 4 such that the image surface 26 is fixed at a predetermined position.
However, in the prior art zoom lens of the above described arrangement, if it is necessary to raise the half angle of view to 30.degree. or more, it becomes difficult to perform aberration correction especially at a side of wide angle, thereby resulting in a drawback that high image quality cannot be achieved over an entire zoom range.